Communicating data or other information between a central location and remotely located data terminals, such as automatic bank teller machines or the like, using conventional telephone lines or data channels is old in the art. A configuration used to provide such communication capability utilizes serially connected unidirectional or simplex data channels between each remotely located data terminal. The first and last data terminals were subsequently connected to the central location to form a serial, closed loop communication system. The success of this configuration require the continued serial operation of a number of components; including, each data channel, each remote terminal, and the electronic circuitry at each termination of the data channel used to modulate and demodulate the data on the data channel. A failure of any one of these components rendered the entire configuration inoperable. Because remote terminals may be widely distributed within a particular location, as for example, at different geographical locations within a city, the common carrier providing the simplex data channels may regard each remote data terminal as a separate and independent data circuit. As such, remedial service for this serial configuration may be provided by numerous field personnel from the common carrier based at the geographic location of each remote data terminal. Thus, a configuration with N data terminals may require N different service locations to isolate a failure to a particular data channel or a particular remote data terminal, or to satisfactorily demonstrate that all data channels are operating correctly.
Regardless of a common carrier's ability or inability to provide field service personnel to identify and resolve problems, a significant disadvantage of this serial, closed loop configuration is the lack of a central point from which all data channels emanate, or to which all data channels arrive. A simple continuity test verifying the integrity of the closed loop configuration becomes virtually impossible to perform from a single central location. Thus, fault identification and isolation becomes slow and cumbersome, and restoration of the communication configuration must await identification and repair of all the failed components.
Another configuration solving the problems of the aforementioned serial, closed loop configuration interconnected each remote data terminal to the central location with a bidirectional or duplex data channel. Adjacent remote data terminals were interconnected to each other essentially by interconnecting the transmit and receive portions of adjacent data channels. However, interconnecting adjacent remote data terminals cannot be accomplished by simply interconnecting the transmit and receive portions of adjacent duplex data channels. This is partially due to the fact that the remote data channels provided by the common carrier attenuate the data propagated along the data channel. In addition, an impedance mismatch may occur between the remote data terminal internal electronics and the characteristic impedance of the data channel making such a direct interconnection virtually impossible. To more effectively utilize the duplex configuration, an active and sophisticated device or communication module must provide the interface between adjacent remote data terminals, the data channels, and the central location.
The present invention provides such a communication module. By having a plurality of data and signal ports, the present invention provides the requisite interfaces for both the remote data terminal and a loop controller within the central location. Circuitry within the module ensures the data propogated along the data channel interfaces with either an associated data terminal, another communication module, or the loop controller. A switching means provides a capability to easily and quickly switch around a failed component so that data communications with other remote data terminals may be continued. Finally, means within the present invention provides a capability to identify the location within the duplex loop configuration at which point a failure has occurred.
Sarle, U.S. Pat. No. 4,035,770 discloses, in part, a switching system for use with a plurality of data terminals connected in series in a loop. The disclosed system does not regenerate the data communicated for subsequent transmission to another data terminal, or another like system, nor does the reference provide a diagnostic capability to identify the point and component at which a loop failure has occurred. The patent to Hackett, U.S. Pat. No. 3,958,111 discloses a commandable diagnostic controller to autonomously simulate data received over an out-of-service data path. The disclosed system provides for a remote device which interfaces redundant data paths, and performs and reports a number of remote tests of digital switching apparatus along one of those data paths. The disclosed system does not provide for the transmission of information, nor does the reference detect impairment in the data channel or provide means for testing the data channel itself.